Field of the Invention
The present disclosure relates to a liquid discharge head that discharges liquid, a liquid discharge apparatus that includes the liquid discharge head, and a method of manufacturing the liquid discharge head.
Description of the Related Art
There is an ink jet printing apparatus, serving as an example of a liquid discharge apparatus, including a liquid discharge head in which energy-generating elements in the liquid flow paths are driven to add energy to liquid inside the liquid flow paths and liquid is discharged from discharge ports onto a printing medium. U.S. Pat. No. 7,837,887 discloses a method of forming liquid supply passages serving as through holes in a substrate of a liquid discharge head. In the above method, a wafer (a silicon substrate) that includes first and second flat surfaces is prepared, a plurality of first flow paths are formed from the first flat surface by etching, and a second flow path that is connected to the first flow paths is formed by etching from the second flat surface towards the first flat surface. The portions in which the first flow paths and the second flow path are connected to each other constitute liquid supply paths that penetrate the substrate. It is desirable to form the first flow paths and the second flow path by reactive ion etching (RIE) that is a type of dry etching since through holes perpendicular to the substrate can be formed using an etching gas. Typically, reactive ion etching is a method of forming a predetermined shape by introducing a reactant gas inside a process chamber and turning the reactant gas into plasma, and using the reactant gas turned into plasma to etch the treatment surface of the substrate. Specifically, the substrate is fixed to a lower electrode inside the process chamber with, for example, an electrostatic chuck and reactant gas is supplied from micropores of an upper electrode to which a high frequency power source is connected between the lower electrode. The supplied reactant gas is turned into plasma between the upper electrode and the lower electrode and etches the substrate such that a predetermined shape is formed.
As illustrated in FIG. 7A, it is known that when forming flow paths using reactive ion etching described above after disposing an etching mask 41 on a substrate 11, the bottom surface of the flow path turns into a rounded shape as illustrated in FIGS. 7B and 7C. This is because the amount of etching gas (etchant) contributing to etching supplied to the center portion of the etching pattern and the amount supplied to the edge portion of the etching pattern are different. In FIG. 7B, solid line arrows illustrate that the amount of etchant supply is high and broken line arrows illustrate that the amount of etchant supply is low. When assuming that the second flow path 13 is a common flow path and the first flow paths 12 are independent flow paths that are in communication with the common flow passage, as illustrated in FIG. 7C, since the bottom portion of the second flow path, that is, the bottom portion of the common flow path has a rounded shape, the length of the plurality of independent flow paths in communication with the bottom portion are not uniform. In other words, a difference of ΔL is created between a length L of the first flow paths 12 in communication with the portion around the center (near the center portion) of the second flow path 13 and the length L′ of the first flow path 12 in communication with the portion around the outside (near the peripheral portion) of the second flow path 13. Specifically, while it depends on the etching conditions, when the second flow path 13 is formed by etching with an etching amount E of about 500 μm, a length difference ΔL of about 10 to 200 μm is created.
In an ink jet printing apparatus that is a type of liquid discharge apparatus, in order for high-speed recording, one may conceive of increasing the discharge frequency of the liquid discharge head. The upper limit of the discharge frequency is determined by the time (refill time) it takes for the liquid to be supplied to the liquid chamber 14 that leads to the discharge ports 17 and to be filled after discharge of liquid. As the refill time becomes shorter, recording can be performed with higher discharge frequency. Furthermore, it is considered that, in order to obtain a printed image with a high definition, it is effective to adopt a method that improves the resolution by making the volume of the discharged liquid small and narrowing the arrangement intervals of the discharge ports 17. In particular, discharge of uniform and small volume droplets and accurate application onto the printing medium are required. Conversely, as described above, when the lengths of the plurality of independent flow paths (first flow paths 12) are different, since each flow path resistance to the corresponding energy-generating element 15 from each individual flow path is different, it is difficult to stabilize the refill time and perform stable discharge of uniform and small volume droplets.
Accordingly, the present disclosure provides a liquid discharge head, a liquid discharge apparatus, and a method of manufacturing the liquid discharge head, in which variation in flow path resistance of flow paths that are connected to discharge ports are small.